In general, capacitive sensors are intended to replace mechanical buttons, knobs, and other similar mechanical user interface controls. Capacitive sensors allow the elimination of such complicated mechanical controls and provide reliable operation under harsh conditions. Capacitive sensors are also widely used in modern customer applications, providing new user interface options in existing products.
Capacitive sensing systems generally operate by detecting a change in the capacitance of a capacitive sensor resulting from proximity or contact of an object with the sensor. The ability to resolve changes in capacitance may be impaired if the changes in capacitance to be detected by the sensor are small relative to the capacitance of the sensor.
For instance, a capacitive sensor that is configured to detect an input, such as proximity or contact with a finger or other object, may have a capacitance CP when no input is present. The capacitance CP is known as the parasitic capacitance of the sensor. An input detected by the sensor may cause a change in capacitance CF that is much smaller than CP. Accordingly, the parasitic capacitance CP is represented by a larger proportion of the discrete capacitance levels resolvable by the bitstream, while the capacitance change CF is represented by fewer of these discrete levels. In such cases, the capacitance change CF due to an input may not be resolvable to a high degree of resolution.